(a) Field of the Invention
The present invention relates to a hydraulic control system and method of an automatic transmission.
(b) Description of the Related Art
A typical automatic transmission uses solenoid valves to supply hydraulic pressure to operational elements (i.e. clutches and brakes) to change gears. Malfunction of the transmission is diagnosed by operating a specific one of the solenoid valves before starting the engine to form line pressure for an N→D speed change. The solenoid valve plunger is abruptly operated, creating noise which is amplified through the valve body. As shown in FIG. 4 at A, when the key is inserted into the ignition switch, a noise of about 25 dB occurs at an operating frequency of 300 Hz of the solenoid valve, and at B, a noise of about 24 dB occurs at an operating frequency of 700 Hz.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.